The invention relates to processing of video signals and more particularly for systems and methods for maintaining consistent video levels when digitizing video signals using different video capture devices.
In the production of video programs, such as television programs and motion pictures, it is common for source material to be digitized with two different video capture devices. For example, one editing system with one video capture device may be used to make a rough cut of the program, while another, usually more sophisticated, editing system with a different video capture device may be used to finish the project. An editing system also may be upgraded to have a new video capture device. In some cases, the video program is produced in two different locations, using two editing systems with two different video capture devices. Sometimes two different video capture devices in the same location are used by systems which perform different tasks. Multiple video capture devices may be used to digitize video for storage on a shared server, from which playback may occur.
A video capture device digitizes analog video signals to provide digital video information. Video signals must have certain levels for various characteristics in order to comply with broadcast and recording industry standards for image quality. For a composite analog signal, these characteristics are gain (contrast), black (brightness or offset), saturation and hue. For a component analog signal, these level settings typically include luma gain (contrast) and luma black (brightness or offset) settings, and gain settings for the red and blue color difference components. A video capture device typically has a mechanism for adjusting settings that control these video levels. These settings initially are preset for several standards such as PAL and NTSC by the manufacturer of the video capture device so that each video capture device provides a generally uniform response. A user also may change the preset settings. These preset settings are called default settings. These settings may be adjusted during digitization of source material, by an editor or automatically, to ensure compliance with industry standards. These adjustments usually are required for each source and result in different settings for each source. It is common to save the adjusted video level settings used to digitize each source in order to reuse them if the source is redigitized using the same video capture device.
Since each video capture device has unique settings due to manufacturing and calibration tolerances, the particular settings for a source digitized on one video capture device may not provide the same video characteristics if used on a different video capture device to digitize the same source. In particular, the internal digital levels provided by the video capture devices in response to certain input settings may not be consistent with each other. For example, for one set of video level settings, the color or brightness of the digitized source material generated by one video capture device may appear correct while the color or brightness of redigitized source material generated by another video capture device with the same video level settings may appear incorrect.
Different types of video capture devices also may have different resolutions or ranges for representing a setting. For example, the gain setting on one type of device may have a range from 0 to 63 while the gain setting on another type of device may have a range from 0 to 255. In such a case, a gain setting for one type of device simply cannot be used directly on devices of another type.
For these reasons, when two video capture devices are used to produce a video program, each video capture device typically must be adjusted for each source, potentially incurring significant costs.
The invention overcomes the need to adjust the video level settings of different video capture devices for each source by saving each setting as a difference between the actual setting and a default setting when digitizing source material. These saved differences are called differential settings. An actual setting for another capture device that provides consistent video levels when digitizing the same source may be derived from both the differential setting obtained when digitizing using the first capture device and the default setting of the other capture device. As a result, source material is mapped to consistent internal digital levels when used on the different devices. Accordingly, video characteristics such as gain, black, saturation and hue can be maintained correctly regardless of the unique settings due to manufacturing and calibration tolerances of the different video capture devices.
Accordingly, in one aspect, video is digitized using a first video capture device such that consistent levels for characteristics of the video are obtained when the video is digitized on a second video capture device. The first video capture device has default settings for the video characteristics. These default settings may be adjusted and the video sequence is digitized using the adjusted settings. Video level settings are stored as differential settings with respect to the default settings. The differential settings may be determined by comparing the adjusted video level settings to the default settings. The video level settings of the second video capture device may be set using the differential settings and default settings for the second video capture device to digitize the video.
In another aspect, video is redigitized so that substantially the same characteristics of the video as digitized with a first video capture device are obtained when using a second video capture device. Differential settings with respect to default settings for the first video capture device are obtained. The video settings of the second video capture device are derived from the differential settings and default settings for the second video capture device. The video sequence is then redigitized using the second video capture device.
In order to set the video settings on the second video capture device, the default settings for the second video capture device may be read. The differential settings may be added to the default settings for the second video capture device to obtain a sum. The video level settings of the second video capture device may be set to the sum of the differential and default settings. In some cases, the differential settings may be scaled according to any difference in range of video level settings between the first video capture device and the second video capture device. The scaled differential settings are added to the default settings of the second video capture device to obtain the new settings.